Metal oxides are utilized for a number of applications, such as gaseous and aqueous pollution control systems, steel manufacture, batteries and catalytic converters, to name a few. Of particular, but not exclusive, interest to Applicants is the use of oxides of manganese in air pollution control systems, water filtration, and respirator applications. Applicants are co-inventors of the subject matter of issued U.S. Pat. Nos. 6,579,507 and 6,610,263, the disclosures of which are incorporated herein by reference. These patents disclose pollutant removal systems and processes, sometimes referred to as Pahlman Process™ Technology, which utilize dry and wet removal techniques and combinations thereof, incorporating the use of oxides of manganese as a sorbent for capture and removal of target pollutants from gas streams.
Metal oxides have the ability to capture target pollutants from gas streams; however, the low pollutant loading rates achieved with various prior art metal oxides have made some industrial applications of this attribute uneconomical. The low target pollutant loading rates of various prior art metal oxide sorbents would require voluminous amounts of sorbent to effectively capture large quantities of target pollutants that exist at many industrial sites, e.g., NOX and/or SO2. The large quantity of sorbent that would be required to capture NOX and/or SO2 could result in an overly costly pollutant removal system, sorbent regeneration system, and waste removal system. It would therefore be desirable to enhance the loading capacities of the metal oxide sorbent in order to economically implement a pollution removal system utilizing metal oxide sorbents.
Metal oxides are also useful in removing pollutants from aqueous streams. However, limitations of prior art metal oxides again result in disappointing pollutant removal performance and marginal economic return. As an example, arsenic is found in water in two common forms or species, arsenite (As+3) and arsenate (As+5). Metal oxides of conventional systems have difficulty in removing arsenite, and costly provisions are often necessary to oxidize the arsenite to arsenate that may be more easily removed. Further, Applicants are not aware of any current technology that can remove arsenite and/or arsenate along with selectively removing hardness in the form of calcium, magnesium, and/or other hardness minerals.
Personal protective respirators also use metal oxides, amongst other materials, in filter elements to capture pollutants and toxins present in various environments to reduce human exposure risks and concerns. Sorbents and filtration media used in conventional filter elements may have a low affinity for certain pollutants requiring more media to ensure removal of pollutants to safe levels. These conventional media may also have low loading capacities that require frequent replacement of the filter cartridge media to prevent breakthrough of the pollutant or toxin.
Metal oxides processed according to the various embodiments of the methods of the invention may exhibit high loading capacities and/or oxidation potential, may be useful as sorbents or filtration media for removal of pollutants from gaseous and aqueous process streams, or may be used to remove arsenite and/or arsenate as well as hardness from aqueous streams, or may be used as filter media in respirators.